THE OPEN-HEARTH FURNACE. 123
chambers Ez and FZ) through which the products of combustion pass to the stack. After the brickwork in the first set of chambers has been partially cooled by the incoming gases, the currents are reversed by means of suitable valves, and the gas and air enter the furnace by way of the chambers $2 and F2, which, as just stated, have been heated by the products of combustion. It will be evident that on every reversal the temperature of the furnace will be higher, for not only will there be the normal increment due to the continued action of the flame which would obtain in any system, but there is another action peculiar to a regenerative construction, for the gases passing through the chambers are hotter on every change in the currents and produce a more intense temperature in combustion. Thus the action is cumulative, and there, is a constant increment of heat throughout the whole construction.
In the case of a furnace which has an insufficient supply of fuel and which contains a full charge of metal, the increased radiation at high temperatures may prevent the attainment of too high a heat; but in a good furnace the action is so rapid that the supply of gas and air must be carefully regulated, in order that radiation can maintain an equilibrium. This necessary control of temperature places a limit on the heat of the regenerators, so that they are usually at about 1800° F. (say 1000° C.). Dissociation plays no part in the operation,, for,, with common producer gas and air, both admitted to the valves at a temperature of about 60° F. (16° 0.), the melting chamber may easily' fuse a very pure sand into viscous porcelain. One such specimen of fused material showed the following composition, in per cent.: Si02, 98.82; A120S, 0.9; Fe203, 0.2.
SEC. Vlllb.—Quality of the gas required.—The system of regeneration, which supplies the furnace with a fuel already raised to a yellow heat, renders unnecessary any stringent specifications regarding the quality of the gas. Ordinary producer gas contains over 60 per cent, of non-combustible material, and yet is all that can be desired, as far as thermal power is concerned. Sulphurous acid and steam are objectionable, but rather_ from their chemical action upon the metal than from any interference with calorific development. Sulphur in large amounts causes trouble, as it is absorbed by the steel.
Steam gives rise to increased oxidation of the metalloids and a